CN102196552A

CN102196552A - Method and system for uplink synchronization of multiple terminals

Info

Publication number: CN102196552A
Application number: CN2010101396652A
Authority: CN
Inventors: 戴谦; 张银成
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2010-03-17
Filing date: 2010-03-17
Publication date: 2011-09-21
Anticipated expiration: 2030-03-17
Also published as: CN102196552B

Abstract

The invention discloses a method for uplink synchronization of multiple terminals, comprising the following steps: selecting terminals with the same uplink synchronization information from the multiple terminals; and keeping uniform uplink synchronization for the selected terminals. The invention also discloses a system for uplink synchronization of multiple terminals. In the system, a selecting unit is used for selecting the terminals with the same uplink synchronization information from the multiple terminals; and an uplink synchronization unit is used for keeping the uniform unlink synchronization for the selected terminals. The method and system can be used to reduce system resource occupancy and system load.

Description

Method and system for uplink synchronization of multiple terminals

Technical Field

The present invention relates to the field of wireless communication technologies, and in particular, to a method and a system for uplink synchronization of multiple terminals in a wireless network.

Background

In an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) of a Long Term Evolution (LTE) system for third generation mobile communication, uplink data is transmitted through a Physical Uplink Shared Channel (PUSCH). Uplink radio resources are allocated to each user terminal by an Evolved node b (eNB). The access technology adopted by the E-UTRAN is Orthogonal Frequency Division Multiplexing (OFDM) technology, and compared with a second generation mobile communication system, the radio resource management of the E-UTRAN system has the characteristics of large bandwidth and multiple time processes, and the radio resource of the E-UTRAN system appears in two dimensions of time and Frequency, so that the number of users which can be carried is greatly increased.

In the LTE system, it is required that the frame boundaries of the uplink signals of all users are aligned when reaching the receiving end of the base station, so as to avoid mutual interference between the received signals. However, since the distances between the ues and the base station are different, that is, the air propagation distances of the uplink signals of the ues are different, the frame boundaries of the uplink signals of the ues cannot be aligned when reaching the receiving end of the base station. In the LTE system, in order to solve this technical problem, an uplink synchronization technology is adopted.

The method for obtaining synchronization of uplink signals of an LTE system belongs to an uplink synchronization method controlled by a base station, namely, a base station dynamically sends timing advance to a user terminal, the user terminal carries out timing advance adjustment on the sending time of the uplink signals according to the timing advance, the signals reach a receiving terminal from a sending terminal to generate propagation delay, and the timing advance is used for offsetting the propagation delay, so that the uplink signals sent by the user terminal can be aligned with the frame boundary of downlink sending signals of the base station after reaching the receiving terminal of the base station side, and synchronization is achieved, as shown in figure 1. By using the technology, the frame boundaries of the uplink signals of all the user terminals linked with the base station, which reach the base station side, are aligned through the control of the base station.

The uplink signal synchronization method of the LTE system is roughly divided into an initial synchronization stage and a synchronization maintenance stage. Wherein, the initial synchronization stage is completed by a random access process, and the function is to realize the large-scale synchronization of the uplink signals; the synchronization maintaining stage is completed by measuring the reference signal in the uplink signal after the random access process is completed, and the function is to realize the small-scale synchronization of the uplink signal. Wherein the uplink Reference Signal includes a pilot Reference Signal (SRS) and a DeModulation Reference Signal (DMRS).

The step that the user terminal completes the initial synchronization stage through the random access process comprises the following steps:

firstly, the user terminal measures the downlink synchronous signal sent by the base station, and measures the time position of the downlink synchronous signal, thereby calculating the frame boundary of the received downlink signal, and taking the frame boundary as the downlink synchronous timing. The specific measurement technique for the time position of the downlink synchronization signal is out of the scope of the present invention, and is not described in detail here.

The user terminal uses the downlink synchronous timing as the uplink signal transmission frame boundary to transmit the random access prefix (Preamble).

After receiving the random access prefix, the base station measures the difference value between the timing of the random access prefix and the boundary of a downlink signal frame, thereby obtaining the initial synchronization timing advance; the base station sends the timing advance to the user terminal through a random access response message.

The user terminal carries out timing advance adjustment on the uplink signal transmitting time boundary according to the timing advance, namely, the user terminal carries out advance adjustment according to the timing advance on the basis of the original transmitting boundary, thereby counteracting the uplink propagation delay, and leading the time when the uplink signal reaches the base station side to be aligned with the downlink signal frame boundary of the base station, namely, the uplink synchronization is achieved.

The timing advance is used as the initial timing advance of the uplink synchronization of the user terminal. When the small-scale timing advance is received subsequently, the small-scale timing advance is accumulated on the initial timing advance, and so on.

When the user terminal transmits the uplink signal, the timing advance used is the accumulated timing advance.

After the ue successfully completes the random access, the ue and the base station establish an RRC link through a Radio Resource Control (RRC) layer link establishment procedure. The specific procedure for establishing the RRC link is not within the scope of the present invention and will not be described in detail herein. In the process of establishing RRC connection, a base station sends configuration information related to physical channel resources to a user terminal through RRC signaling, and the user terminal configures the corresponding physical channel resources according to the configuration information. These pieces of configuration information include configuration information of the pilot reference signal, and the user terminal transmits the uplink pilot reference signal as specified by the configuration information.

The step of the synchronization maintenance phase of the uplink carrier comprises:

a base station obtains a small-scale timing advance measurement result according to measurement of a reference signal, namely SRS or DMRS (a specific measurement technology is not in the scope of the invention and is not detailed), and sends the timing advance value to a user terminal through a Media Access Control element (MAC CE); as for the measurement of SRS or DMRS, the specific measurement technique is out of the scope of the present invention and is not described in detail here.

The ue adds the value of the timing advance to the value of the timing advance adjusted last time, that is: and the timing advance (n +1) is the timing advance (n) + the timing advance measured at the current moment, and the user terminal performs timing advance adjustment on the uplink signal transmission frame boundary according to the accumulated timing advance.

The user terminal needs to know the frequency point information, bandwidth information, random access channel resource configuration information and other system information of the target uplink carrier in the process of finishing uplink synchronization, and the system information is all broadcast by the base station through a broadcast channel or sent to the user terminal through a wireless resource control signaling.

In order to further enhance the application range of the communication system, the concept of the internet of things is introduced and widely promoted in the standard meeting of the communication industry. The internet of things in a broad sense includes both traditional human-to-human communication (H2H, human to human) and Machine-to-Machine communication (M2M, Machine to Machine). In the 3Gpp conference, M2M is also entitled "Machine Type Communication," MTC for short. With the introduction of the M2M concept, communication services are expanded in various aspects. Such as smart home, smart transportation, smart metering. The intelligent home comprises remote control of home appliances, remote monitoring of home security and the like; the intelligent traffic comprises traffic flow monitoring, accident monitoring, vehicle monitoring and the like; the intelligent metering comprises monitoring and remote control of an industrial instrument, remote meter reading and the like.

There are many terminal types in the application of the internet of things, wherein a large percentage of the terminals are fixed terminals, such as household water meters and electric meters; pressure gauge, flowmeter, etc. in industrial production. In addition, there are a lot of terminals which are not fixed in position but have limited area, and the term "limited area" as used herein means that the distance from a terminal to a central position cannot exceed a certain range, such as a tracking device installed on a vehicle, a subway, a train, a ship, a payment terminal, and the like.

Because the types of the devices of the internet of things are wide and the number of the devices is large, great pressure is applied to a communication system, for example, when a large number of devices of the internet of things are linked with a base station, a large amount of wireless resources are occupied, and signaling congestion and data congestion are caused. In addition, in order to maintain uplink synchronization of these terminals, the base station needs to issue a large number of synchronization adjustment commands and perform a large number of synchronization measurements, which all cause a large burden on the system. In summary, the existing uplink synchronization technology is: aiming at uplink synchronization respectively performed by a single terminal, after the concept of the internet of things is introduced, the terminals of the internet of things are numerous, and the uplink synchronization technology still occupies a large amount of system resources and increases system load. At present, an improved uplink synchronization technology is urgently needed, and system resource occupation and system load can be reduced.

Disclosure of Invention

In view of the above, the main objective of the present invention is to provide a method and a system for uplink synchronization of multiple terminals, which can reduce system resource occupation and system load.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a method for uplink synchronization of multiple terminals includes: selecting a terminal with the same uplink synchronization information from a plurality of terminals; and performing unified uplink synchronization maintenance on the selected terminals.

Wherein the uplink synchronization information includes: adjusting the uplink frame synchronization time; the method further comprises the following steps: and determining the terminals with the same uplink frame synchronization time adjustment amount as a synchronization terminal group.

Wherein, in the sending stage when the unified uplink synchronization is maintained, the method further comprises: the network side sets one or more network identifications, and the base station selects one network identification corresponding to the synchronous terminal group from the set network identifications; the base station sends the selected network identification to all terminals in the synchronous terminal group; and the base station sends the uplink frame synchronization time adjustment quantity to all terminals in the synchronization terminal group.

Wherein, in the receiving stage when the unified uplink synchronization is maintained, the method further comprises: and all the terminals in the synchronous terminal group receive corresponding uplink frame synchronous time adjustment quantity according to the received network identification.

Wherein the uplink frame synchronization time adjustment amount comprises: adjusting quantity of uplink frame synchronization relative time or adjusting quantity of uplink frame synchronization absolute time; wherein, the uplink frame synchronization relative time adjustment amount is: relative adjustment value of the adjustment quantity of the uplink frame synchronization absolute time relative to the current terminal;

when receiving the uplink frame synchronization time adjustment amount, the method further includes: and adjusting the sending time boundary of the uplink frame according to the uplink frame synchronous absolute time adjustment quantity.

Wherein, the method also comprises: selecting terminals with the same uplink frame synchronization time adjustment amount from a plurality of terminals in a preset mode at a base station side;

the preset mode of the base station side comprises any one of the following modes:

mode 1: when the distance between two terminals is smaller than a preset threshold, setting the uplink frame synchronization absolute time adjustment quantity of the two terminals to be the same;

mode 2: when the distances from a group of terminals to the center position are all smaller than a preset threshold, setting the uplink frame synchronization absolute time adjustment quantity of the group of terminals to be the same;

mode 3: and when the distances between every two terminals of a group are smaller than a preset threshold, setting the uplink frame synchronization absolute time adjustment quantity of the group of terminals to be the same.

Wherein, the method also comprises: selecting terminals with the same uplink frame synchronization time adjustment amount from a plurality of terminals in a base station side measurement mode;

the mode of the base station side measurement comprises any one of the following modes:

mode 1: the base station measures the uplink frame synchronization time adjustment quantity required by each terminal in the plurality of terminals to keep uplink synchronization; when the uplink frame synchronization absolute time adjustment quantities of a plurality of terminals are found to be equal in a preset time period or the number of continuous equal times exceeds a preset threshold, the uplink frame synchronization absolute time adjustment quantities of the plurality of terminals are known to be the same, and a synchronization terminal group is formed;

mode 2: the base station measures the uplink frame synchronization time adjustment quantity required by a current terminal to maintain uplink synchronization in a plurality of terminals, and compares the measured uplink frame synchronization time adjustment quantity of the current terminal with the uplink frame synchronization time adjustment quantity of the existing synchronization terminal group; when the uplink frame synchronization absolute time adjustment quantity of the current terminal is found, and the uplink frame synchronization absolute time adjustment quantity of the synchronization terminal group are kept equal in a preset time period or the number of continuous equal times exceeds a preset threshold, the uplink frame synchronization absolute time adjustment quantities of the current terminal and the synchronization terminal group are known to be the same, and the terminal can be added into the synchronization terminal group.

When the base station sends the selected network identifier to all terminals in the synchronous terminal group, the method further comprises: the network identifier is sent through a Radio Resource Control (RRC) dedicated signaling, or the network identifier is sent through a Media Access Control (MAC) control unit, or the network identifier is sent through a physical downlink control channel.

Before the base station sends the uplink frame synchronization time adjustment amount to all terminals in the synchronization terminal group, the method also comprises the step of obtaining the uplink frame synchronization time adjustment amount;

the implementation manner of the acquisition includes any one of the following manners:

mode 1: when a terminal type with a fixed position exists in a synchronous terminal group or a terminal type with an unfixed position but a limited area exists in the synchronous terminal group, the base station selects a terminal in the two terminal types in a fixed manner, a random manner or a rotation manner; measuring the selected uplink reference signal or uplink synchronous signal of the terminal; determining the uplink frame synchronization time adjustment quantity of the terminal obtained according to the measurement as the uplink frame synchronization time adjustment quantity of the whole synchronization terminal group;

mode 2: when only mobile terminal types with unlimited areas exist in the synchronous terminal group, the base station measures uplink reference signals or uplink synchronous signals of all terminals in the synchronous terminal group; and determining the uplink frame synchronization time adjustment quantity of the whole synchronization terminal group as the uplink frame synchronization time adjustment quantity of the whole synchronization terminal group, wherein the uplink frame synchronization time adjustment quantity is the largest in the selected uplink frame synchronization time adjustment quantities with the same quantity.

When the base station sends the uplink frame synchronization time adjustment amount to all terminals in the synchronization terminal group, the method further comprises: the uplink frame synchronization time adjustment quantity is sent through a physical downlink control channel; the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

When the base station sends the uplink frame synchronization time adjustment amount to all terminals in the synchronization terminal group, the method further comprises: the uplink frame synchronization time adjustment quantity is sent through a physical downlink shared channel indicated by a physical downlink control channel; the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

The uplink frame synchronization time adjustment amount is specifically an uplink frame synchronization absolute time adjustment amount; the method further comprises the following steps: when the base station keeps measuring the uplink reference signal or the uplink synchronous signal of the mobile terminal with unlimited area in the synchronous terminal group, if the uplink frame synchronous absolute time adjustment quantity of the current terminal is judged to be asynchronous with the uplink frame synchronous absolute time adjustment quantity of the synchronous terminal group, the current terminal is removed from the synchronous terminal group.

Wherein, judging that the asynchronization specifically includes:

when the times that the uplink frame synchronization absolute time adjustment quantity of the current terminal and the uplink frame synchronization absolute time adjustment quantity of a synchronization terminal group to which the current terminal belongs are different from each other are up to a preset threshold within a preset time period are measured by the base station, the current terminal and the synchronization terminal group are judged to be out of synchronization; wherein the preset threshold is an integer greater than 0.

Wherein, judging that the asynchronization specifically includes: when the base station measures the uplink frame synchronization absolute time adjustment quantity of the current terminal and the occurrence of different continuous times of the uplink frame synchronization absolute time adjustment quantity of a synchronization terminal group to which the current terminal belongs reaches a preset threshold, judging that the current terminal is out of synchronization with the synchronization terminal group; wherein the preset threshold is an integer greater than 0.

Wherein the removing of the current terminal from the synchronization terminal group specifically comprises: the base station informs the current terminal through a special signaling, and the current terminal releases the network identification corresponding to the synchronous terminal group after receiving the special signaling.

Wherein the removing of the current terminal from the synchronization terminal group specifically comprises: and the base station sends the uplink frame synchronization absolute time adjustment amount to the current terminal in a conventional mode, and after receiving the uplink frame synchronization absolute time adjustment amount, the current terminal determines that the current terminal is removed from the synchronization terminal group and releases the network identifier corresponding to the synchronization terminal group.

A system for uplink synchronization of multiple terminals, the system comprising: a selection unit and an uplink synchronization unit; wherein,

a selecting unit, configured to select a terminal having the same uplink synchronization information from among the plurality of terminals;

and the uplink synchronization unit is used for uniformly maintaining the uplink synchronization of the selected terminals.

The selection unit is further configured to select a terminal with the same uplink frame synchronization time adjustment amount from the multiple terminals;

the system further comprises: and the determining unit is used for determining the terminals with the same uplink frame synchronization time adjustment amount as a synchronization terminal group.

In a sending stage when the unified uplink synchronization is maintained, the uplink synchronization unit further includes a sending module configured to set one or more network identifiers on a network side, and the base station selects a network identifier corresponding to the synchronization terminal group from the set network identifiers; the base station sends the selected network identification to all terminals in the synchronous terminal group; and the base station sends the uplink frame synchronization time adjustment quantity to all terminals in the synchronization terminal group.

In the receiving stage when the unified uplink synchronization is maintained, the uplink synchronization unit further includes a receiving module, configured to receive, by all terminals in the synchronization terminal group, corresponding uplink frame synchronization time adjustment amounts according to the received network identifier.

The selection unit further realizes the selection in a preset mode at the base station side;

The selection unit further realizes the selection in a mode of base station side measurement;

Selecting a terminal with the same uplink synchronous information from a plurality of terminals; and uniformly maintaining uplink synchronization of the selected terminals.

The invention can realize uplink synchronization for multiple terminals and uniformly maintain uplink synchronization for multiple terminals with the same uplink synchronization information, thereby greatly saving the system overhead of maintaining uplink synchronization while maintaining uplink synchronization and achieving the purpose of reducing system resource occupation and system load.

Drawings

Fig. 1 is a schematic diagram of existing uplink synchronization in an LTE system;

FIG. 2 is a schematic view of a scenario of embodiment 1 of the present invention;

fig. 3 is a flowchart of establishing a synchronization terminal group according to embodiment 1 of the present invention;

fig. 4 is a flowchart of a terminal joining and exiting an existing synchronization terminal group according to embodiment 1 of the present invention;

FIG. 5 is a diagram illustrating a scenario of embodiment 2 of the present invention;

fig. 6 is a schematic diagram of a timing process of synchronous terminal group switching according to embodiment 2 of the present invention;

FIG. 7 is a diagram illustrating a scenario of embodiment 3 of the present invention;

fig. 8 is a flowchart illustrating a construction of a mobile terminal synchronization terminal group of a non-area-limited type according to embodiment 3 of the present invention.

Detailed Description

The basic idea of the invention is: selecting a terminal with the same uplink synchronization information from a plurality of terminals; and uniformly maintaining uplink synchronization of the selected terminals.

The following describes the embodiments in further detail with reference to the accompanying drawings.

A method for uplink synchronization of multiple terminals mainly comprises the following steps:

the base station selects the terminals with the same uplink frame synchronization time adjustment amount in the cell, and if the terminals are a synchronization terminal group, the network side sets one or more network identifiers, and the base station selects one of the network identifiers to correspond to the synchronization terminal group; the base station sends the network identification to all terminals of the synchronous terminal group; the base station only sends one uplink frame synchronization time adjustment quantity to all terminals of the synchronization terminal group so as to keep uplink synchronization of all terminals of the synchronization terminal group. And all the terminals of the synchronous terminal group receive corresponding uplink frame synchronous time adjustment quantity according to the received network identification, and adjust the sending time boundary of the uplink frame according to the uplink frame synchronous absolute time adjustment quantity.

The uplink frame synchronization time adjustment amount sent by the base station can be a relative adjustment amount or an absolute adjustment amount; the relative adjustment amount is as follows: relative adjustment value of absolute time adjustment quantity relative to the current uplink frame synchronization of the terminal.

For uplink synchronization of multiple terminals, where for a terminal whose uplink frame synchronization time adjustment amount in a cell is selected by the base station to be the same, the specific implementation may include: the scheme preset at the base station side and the scheme of base station measurement are set forth below respectively.

Firstly, a scheme preset at a base station side: the scheme is suitable for terminals installed at certain fixed positions, such as anti-theft sensors in buildings, and terminals installed at certain mobile but area-limited places, such as tracking equipment, payment terminals and the like installed on vehicles, subways, trains and ships.

If the distance between the two terminals is smaller than the predetermined threshold, the uplink frame synchronization absolute time adjustment amounts of the two terminals are considered to be the same.

If the distances from a group of terminals to a certain center position are all smaller than a preset threshold, the uplink frame synchronization absolute time adjustment amounts of the group of terminals are considered to be the same.

Or, if the distances between each two terminals in a group are smaller than a predetermined threshold, the uplink frame synchronization absolute time adjustment amounts of the terminals in the group are considered to be the same.

The base station prestores information (equipment identification or IMSI number of the terminal, identification of a synchronous terminal group to which the terminal belongs) of the terminal capable of forming the synchronous terminal group at a network side, and when the terminal accesses the network, the base station judges whether the terminal belongs to the synchronous terminal group and which synchronous terminal group the terminal belongs to according to the stored information; the distance information between the terminals can also be stored in the network side.

Secondly, a scheme for measuring the base station: the scheme can be applied to all types of terminals, namely, the scheme is also applicable to mobile terminals without limited areas, such as mobile phones, portable heart monitors or wild animal trackers and the like, besides the two fixed-position mounted terminals and the terminals with limited areas.

The base station measures the uplink frame synchronization time adjustment quantity required by each terminal to maintain uplink synchronization, and if the uplink frame synchronization absolute time adjustment quantities of a plurality of terminals are found to be equal in a preset time period or the continuous equal times exceed a certain preset threshold, the uplink frame synchronization absolute time adjustment quantities of the plurality of terminals are considered to be the same, and a synchronization terminal group can be formed.

Or, the base station measures the uplink frame synchronization time adjustment quantity required by a certain terminal to maintain uplink synchronization, compares the uplink frame synchronization time adjustment quantity with the uplink frame synchronization time adjustment quantity of the existing synchronization terminal group, and if the uplink frame synchronization absolute time adjustment quantity of the terminal and the uplink frame synchronization absolute time adjustment quantity of the certain synchronization terminal group are found to be equal in a preset time period or the continuous equal times exceed a certain preset threshold, the uplink frame synchronization absolute time adjustment quantities of the terminal and the synchronization terminal group are considered to be the same, and the terminal can join the synchronization terminal group.

For uplink synchronization of multiple terminals, the specific implementation of the base station sending the network identifier to all terminals in the synchronized terminal group may include: sending the network identification through RRC dedicated signaling; transmitting a network identification through a Media Access Control (MAC) control unit; and sending the network identification through a physical downlink control channel.

For uplink synchronization of multiple terminals, where for only one uplink frame synchronization time adjustment sent by the base station to all terminals of a synchronization terminal group, the uplink frame synchronization time adjustment may be obtained in the following manner:

if there is a terminal with fixed position in the synchronization terminal group, or there is a terminal with unfixed position but limited area, the base station may select a terminal in the two types of terminals, either randomly or alternately, to measure the uplink reference signal or the uplink synchronization signal, and the obtained uplink frame synchronization time adjustment amount of the terminal may be used as the uplink frame synchronization time adjustment amount of the whole synchronization terminal group.

And secondly, if only mobile terminals with unlimited areas exist in the synchronous terminal group, the base station measures uplink reference signals or uplink synchronous signals of all terminals in the synchronous terminal group, and selects the uplink frame synchronization time adjustment quantity with the largest quantity from the obtained uplink frame synchronization time adjustment quantities of all terminals as the uplink frame synchronization time adjustment quantity of the whole synchronous terminal group.

For uplink synchronization of multiple terminals, where for only one uplink frame synchronization time adjustment sent by the base station to all terminals of a synchronization terminal group, the sending of the uplink frame synchronization time adjustment can be implemented in the following manner:

firstly, the uplink frame synchronization time adjustment quantity is sent through a physical downlink control channel, and the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

And secondly, the uplink frame synchronization time adjustment quantity is sent through a physical downlink shared channel indicated by a physical downlink control channel, such as a downlink service data channel, and the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

Aiming at uplink synchronization of multiple terminals, the method further comprises the following contents related to measurement:

the base station should keep measuring the uplink reference signal or uplink synchronous signal of the mobile terminal whose area is not limited in the synchronous terminal group, and if the uplink frame synchronous absolute time adjustment quantity of a certain terminal is found to be asynchronous with the uplink frame synchronous absolute time adjustment quantity of the synchronous terminal group, the terminal is removed from the synchronous terminal group.

For the measurement of uplink synchronization of multiple terminals, how to determine that the uplink frame synchronization absolute time adjustment amount of a certain terminal is asynchronous with the uplink frame synchronization absolute time adjustment amount of a synchronization terminal group can be specifically realized in the following manner:

the base station measures the times that the absolute time adjustment quantity of the uplink frame synchronization of the terminal is different from the absolute time adjustment quantity of the synchronization terminal group to which the terminal belongs, and the times reach a certain preset threshold within a preset time, and the terminal and the synchronization terminal group are considered to be asynchronous; the threshold is an integer greater than 0.

Or, the base station detects that the continuous times that the uplink frame synchronization absolute time adjustment quantity of the terminal is different from the absolute time adjustment quantity of the synchronization terminal group reach a certain preset threshold, and then the terminal and the synchronization terminal group are considered to be asynchronous; the threshold is an integer greater than 0.

For the measurement of uplink synchronization of multiple terminals, the specific implementation of how to remove a terminal from a synchronization terminal group can be implemented as follows:

the base station informs the terminal through a special signaling, and the terminal releases the network identification corresponding to the synchronous terminal group after receiving the notice.

Or, the base station sends the uplink frame synchronization time adjustment amount to the terminal by a conventional method, and the terminal considers that the terminal is removed from the synchronization terminal group after receiving the uplink frame synchronization time adjustment amount and releases the network identifier corresponding to the synchronization terminal group; the conventional method is that the base station uses the network identification of the terminal itself instead of the network identification corresponding to the synchronous terminal group to identify the uplink frame synchronization time adjustment amount.

In summary, by using the uplink synchronization technology for multiple terminals of the present invention, a terminal with consistent uplink synchronization among multiple terminals can be selected, and an appropriate method is used to reduce uplink synchronization adjustment signaling sent by the terminal with consistent uplink synchronization, so that while uplink synchronization is maintained, system overhead for maintaining uplink synchronization can be greatly reduced, thereby achieving the purpose of reducing system resource occupation and system load. Moreover, the system overhead for keeping uplink synchronization is reduced, system resources are saved, and the purpose of reducing the system operation complexity can be achieved.

The invention is illustrated below.

Example 1:

the embodiment describes how to establish a synchronous terminal group and maintain uplink synchronization by using terminals with fixed positions and limited areas; the procedure is described for how a mobile, area-unrestricted terminal joins and leaves a group of synchronized terminals.

An example scenario is an LTE system, a cell scenario is as shown in fig. 2, and within a coverage area of a base station, there is a factory, and a plurality of industrial instruments (belonging to M2M devices) are fixedly installed inside the factory and respectively identified by M1 to M7. In addition, a bus is provided, and a plurality of M2M devices (card swiping machines, alarms, traffic monitoring devices and the like) are fixedly installed inside the bus and are respectively identified by M8-M11. As can be seen from the foregoing description, M1 to M7 belong to fixed terminals, and M8 to M11 belong to mobile but area-limited terminals. Passengers on the bus have portable internet of things devices or mobile phones, such as a heart monitor, a portable computer and the like, which are respectively identified by U3 and U4; workers in the factory carry portable Internet of things equipment or mobile phones which are respectively identified by U1 and U2.

In order to support this function, N synchronous radio network temporary identities (SYNC-RNTI) may be configured for each cell on the network side, and the identities may adopt orthogonal sequences, random sequences, or sequences generated by other methods, as long as the identities are not mutually repeated and can be uniquely identified by the network side, and the sequence length is a natural number greater than 1. N is a natural number, the formulation of N depends on the scale of the number of terminals in the network, and the larger the number of terminals is, the larger N should be.

The SYNC-RNTI configured in different cells may be the same or different.

And the network side sets that when the distances from a plurality of terminals to a certain central position are all less than or equal to K, the plurality of terminals can be regarded as a synchronous terminal group. Wherein the central position may be fixed or may be mobile. The value range of K is defined by the following formula (1):

0＜K＜＝C*16Ts/4 (1)

in the formula (1), C is the propagation speed of electromagnetic waves, Ts is the symbol length (3.255 × 10-8 seconds) of the LTE system, and 16Ts is the minimum granularity of an uplink synchronization Time adjustment (TA, also called Time advance) of the LTE system. The calculation result is as follows: k is more than 0 and is 37.65 m. In this embodiment, let K be 30 meters for the cell site.

In fig. 2, M1 to M6 are located in a region with a radius R1, R1 is K, M7 is located outside the region, the distance from the center of the region is d1, and d1 > K. From the above description, it is easily understood that M1 to M6 satisfy the condition for forming a synchronized terminal group, and M7 does not satisfy the condition for forming a synchronized terminal group with other terminals.

Since the length of the bus is usually 12 to 18 meters, assuming that the length of the bus in fig. 2 is 18 meters, the distances from all terminals (M8-M11, U3 and U4) on the bus to the geometric center of the bus are all smaller than the half-length R2 of the bus (R2-18/2-9 meters), and R2 < K meets the condition of forming a synchronous terminal group.

The terminals fixedly installed in factories and the terminals fixedly installed on buses belong to terminals of operators or service providers, and are generally not detached, and such terminals can be classified into 'fixed position' and 'limited area' terminals. Information of such terminals can be stored on the network side. Wherein, the information of the terminal comprises: the equipment identifier or IMSI number of the terminal, and the identifier of the synchronous terminal group to which the terminal belongs; the network side includes: a base station, a core network, or an M2M server. The specific implementation of the storage may be according to the following mode in table 1, where table 1 is a synchronization terminal group mapping table.

TABLE 1

In addition to the method of table 1, other methods may be used for storage as long as the correspondence between the synchronization terminal group and the member terminals can be expressed.

The mobile terminals (U1-U4) with no restricted area cannot be predefined as member terminals of a certain group of synchronized terminals, i.e. cannot be stored in table 1, due to the unpredictability of their location.

The management process of the synchronous terminal group comprises the establishment of the synchronous terminal group, the joining and exiting of member terminals and the switching process of the synchronous terminal group. The first 2 processes are illustrated below, and the handover process of the synchronized terminal group is described in the next embodiment.

Fig. 3 is a flow chart of the establishment of a synchronized terminal group. Assuming that M1-M6 are initially in the power-off state, and then are powered on one by one and establish a connection with the base station, in this process, the synchronized terminal group 1 (refer to fig. 2 and table 1) completes the establishment, and the steps are described as follows:

assuming that M1 is powered on first and establishes connection with the base station, the base station obtains the device information of M1 in the process;

step 101, the base station compares the device identifier of the terminal with table 1.

Step 102, determine whether the device identifier belongs to a synchronization terminal group? If yes, go to step 103; otherwise step 104 is entered. As can be seen from table 1, M1 belongs to synchronized terminal group 1, and therefore, the process proceeds to step 103. If it is M7, step 104 is entered.

Step 103, determine whether the synchronization terminal group is not established? If yes, go to step 105; otherwise step 106 is entered. Since none of the terminals corresponding to the synchronized terminal group 1 remain connected to the base station before the access of M1, the synchronized terminal group 1 is not established yet, and the process proceeds to step 105.

And step 104, the base station maintains the uplink synchronization of the terminal by adopting a conventional method.

Here, the conventional method means: LTE has an existing uplink synchronization maintenance mechanism.

And 105, the base station selects one of the unused SYNC-RNTIs as the identification of the synchronous terminal group, and the synchronous terminal group is established.

Step 106, the base station sends the SYNC-RNTI of the synchronization terminal group (synchronization terminal group 1) to the M2M device, i.e. M1, through RRC signaling.

And step 107, the base station measures an uplink reference signal of a terminal with established connection of the synchronization terminal group in the optional table according to the stored synchronization terminal group corresponding table to obtain an uplink Timing Advance (TA), the base station issues the TA value through the MAC CE, and the PDCCH corresponding to the MAC CE is identified by using the SYNC-RNTI.

Here, currently, in the synchronized terminal group 1 in table 1, only M1 one terminal establishes a connection, and therefore the base station selects the TA value of M1 as the TA value of the synchronized terminal group 1. If more than one terminal corresponding to the synchronized terminal group 1 in table 1 establishes a connection with the base station, the base station may randomly, fixedly or alternately select one terminal from the terminals corresponding to the synchronized terminal group 1, and measure the TA value of the selected terminal as the TA value of the synchronized terminal group 1.

In step 108, the M2M terminal receives the PDCCH according to the SYNC-RNTI and decodes the TA value to maintain uplink synchronization.

Here, M1 decodes PDCCH based on the received SYNC-RNTI of synchronization terminal group 1, obtains TA value in the corresponding MAC CE, adjusts uplink frame boundary, and maintains uplink synchronization.

In fig. 2, the terminals M8 to M11 with limited areas on the bus belong to the synchronization terminal group 2, and the establishment process of the synchronization terminal group 2 is the same as the flow of fig. 3, and the description is not repeated.

Fig. 4 is a flowchart of a terminal joining and leaving an existing group of synchronized terminals. Referring to fig. 2, the mobile terminal U1 enters the range of the synchronized terminal group 1 (the distance from the center position is less than R1), and stays in the area, if the synchronized terminal group 1 is already established, the U1 can join the synchronized terminal group 1. Further, the mobile terminal U2 is initially located within the range of the synchronized terminal group 1, and now moves outward and moves out of the range of the synchronized terminal group 1, and U2 exits the synchronized terminal group 1. The steps are described as follows:

step 201, it is assumed that a certain terminal moves into the range of a certain synchronization terminal group, and the base station finds that the uplink synchronization absolute time adjustment amount of the terminal is always the same as the uplink synchronization absolute time adjustment amount of the synchronization terminal group in the time period T in the process of maintaining the uplink synchronization of the terminal.

Here, the length of T may be preset by the network side and sent to the terminal; in fig. 2, U1 enters the range of synchronization terminal group 1 and satisfies the requirement that the uplink synchronization absolute time adjustment amount of synchronization terminal group 1 is equal to the uplink synchronization absolute time adjustment amount in the T period.

Step 202, the base station adds the terminal into the synchronization terminal group, and sends the SYNC-RNTI corresponding to the synchronization terminal group to the terminal through a dedicated signaling.

Here, step 202 is: the base station adds U1 to the synchronization terminal group 1, and sends SYNC-RNTI of the synchronization terminal group 1 to the terminal through a dedicated signaling, wherein the dedicated signaling can be RRC signaling, PDCCH or MAC CE.

In step 203, the terminal receives the PDCCH according to the SYNC-RNTI and decodes the TA value, thereby completing uplink synchronization.

Here, U1 decodes PDCCH based on the received SYNC-RNTI of synchronization terminal group 1, obtains TA value of synchronization terminal group 1, and maintains its own uplink synchronization.

Step 204, the base station judges whether the terminal is a fixed-position or limited-area terminal according to the information of the corresponding relation table of the synchronous terminal group and the member terminal stored at the network side, if so, the step 206 is entered; if not, go to step 205. According to table 1 stored by the base station, U1 does not exist in table 1, and therefore the base station considers that U1 is not a "fixed location" or "area restricted" type terminal, and proceeds to step 205.

Step 205, the base station keeps periodic measurement of the uplink reference signal of the terminal to track the change of the uplink synchronization absolute time adjustment amount.

Here, step 205 is: the base station needs to keep monitoring the independent uplink synchronization of U1, and for the same reason, the base station also needs to keep monitoring the independent uplink synchronization of U2.

Step 206, the base station does not keep the periodic measurement of the uplink reference signal of the terminal.

Here, for the terminals belonging to table 1, the base station adopts the method as described in step 107, instead of measuring the uplink reference signal for each terminal of table 1.

Step 207, if the uplink synchronization absolute time adjustment amount of a certain terminal is different from the uplink synchronization absolute time adjustment amount of the synchronization terminal group to which the terminal belongs for N consecutive times, the base station sends a special signaling to notify the terminal, and removes the terminal from the synchronization terminal group.

Here, N is an integer greater than 0, and N may be set to 2, for example. In fig. 2, when U2 moves out of the range of synchronized terminal group 1 and its uplink synchronization absolute time adjustment amount is different from that of synchronized terminal group 12 times, the base station transmits dedicated signaling (which may be transmitted through RRC signaling, PDCCH, or MAC CE) to notify U2 to remove it from synchronized terminal group 1.

And step 208, after receiving the notification, the terminal releases the SYNC-RNTI corresponding to the synchronization terminal group. And after receiving the notification, the U2 releases the SYNC-RNTI corresponding to the synchronization terminal group 1.

In fig. 2, the mobile terminal U3 enters the bus and the mobile terminal U4 leaves the bus, which also follow the flow of fig. 4 to implement the process of joining or leaving the synchronized terminal group 2, and the description is not repeated here.

Example 2:

the embodiment describes the canceling and establishing process of the synchronous terminal group when switching occurs.

An embodiment scenario is shown in fig. 5, and the scenario configuration is the same as that of embodiment 1, where the bus where the synchronization terminal group 2 is located leaves the range of the base station a and enters the range of the base station B. In the switching process, the member terminals of the synchronous terminal group 2 of the base station A continuously complete switching, the member terminals of the synchronous terminal group 2 are continuously reduced to 0, and the synchronous terminal group 2 of the base station A is cancelled; accordingly, a synchronized terminal group 2 of the base station B is established. Referring to fig. 6, the process is described as follows:

301. when the bus enters the range of the base station B, the terminal U3 firstly initiates a switching request, and after the base station A receives a switching confirmation fed back by the core network, the U3 is removed from the synchronous terminal group 2.

302. After U3 is handed over to bs B, synchronized terminal group 2 of bs B has not been established (referring to table 1, terminals M8-M11 of synchronized terminal group 2 in table 1 have not been handed over to bs B, and therefore synchronized terminal group 2 is not established), so U3 is not added to any synchronized terminal group.

303. After the M8 enters the handover area, the M8 initiates a handover request, and after the base station a receives a handover confirmation fed back by the core network, the synchronization terminal group 2 is removed from the M8.

304. After the M8 is handed over to the base station B, the base station B finds, by comparing table 1, that M8 belongs to the synchronized terminal group 2 and is the first terminal establishing connection in table 1, which belongs to the synchronized terminal group 2, so that the base station B establishes the synchronized terminal group 2, allocates a SYNC-RNTI to the synchronized terminal group 2, and sends the SYNC-RNTI to M8 through a dedicated signaling.

305. After the synchronization terminal group 2 is established, when detecting the uplink synchronization absolute time adjustment amount of U3, the base station B finds that it satisfies the condition of joining the synchronization terminal group 2 (please refer to example 1), and joins it to the synchronization terminal group 2 (please refer to example 1).

306. After the M9 enters the handover area, the M9 initiates a handover request, and after the base station a receives a handover confirmation fed back by the core network, the synchronization terminal group 2 is removed from the M9.

307. After the M9 is handed over to the bs B, the bs B compares table 1 to find that M9 belongs to the synchronized terminal group 2, and then adds it to the synchronized terminal group 2 (please refer to example 1).

308. After the U4 enters the handover area, the U4 initiates a handover request, and after the base station A receives a handover confirmation fed back by the core network, the U4 is removed from the synchronization terminal group 2.

309. After the U4 is handed over to the bs B, the bs B detects that the uplink synchronization absolute time adjustment amount of the U4 satisfies the condition of joining the synchronized terminal group 2 (please refer to example 1), and joins the uplink synchronization absolute time adjustment amount to the synchronized terminal group 2 (please refer to example 1).

310. After the M11 enters the handover area, the M11 initiates a handover request, and after the base station a receives a handover confirmation fed back by the core network, the synchronization terminal group 2 is removed from the M11.

311. After the M11 is handed over to the bs B, the bs B compares table 1 to find that M11 belongs to the synchronized terminal group 2, and then adds it to the synchronized terminal group 2 (please refer to example 1).

312. After the M10 enters the handover area, the M10 initiates a handover request, and after the base station a receives a handover confirmation fed back by the core network, the synchronization terminal group 2 is removed from the M10.

313. At this point, all the member terminals of the synchronization terminal group 2 of the base station a are offline, and the base station a cancels the synchronization terminal group 2.

314. After the M10 is handed over to the bs B, the bs B compares table 1 to find that M10 belongs to the synchronized terminal group 2, and then adds it to the synchronized terminal group 2 (please refer to example 1).

Example 3:

this embodiment describes: under the condition of no terminal with a fixed position or a limited area, how a base station establishes a synchronous terminal group for a group of movable terminals with unlimited areas after the group of movable terminals meets the condition of establishing the synchronous terminal group; and how to exit the synchronization terminal group when a certain terminal and the synchronization terminal group lose synchronization.

An example scenario is an LTE system (see fig. 7), a plurality of people work in a small office, each person carries 1 or more internet of things devices (U1-U8), and the devices are not "area-limited" terminals. The length and width of the small office is 20 x 20 m,

and (4) rice. The base station side K was set to 30 m (refer to example 1). R is less than K, and according to the invention content, all the Internet of things equipment in the small office can form a synchronous terminal group.

Referring to fig. 8, the construction flow of the mobile and non-area-limited terminal synchronization terminal group is as follows:

step 401, the base station tracks the absolute uplink synchronization adjustment amounts of all terminals, and if it is found that the absolute uplink synchronization adjustment amounts of 2 or more terminals are always equal in the time period T, it is considered that the terminals whose absolute uplink synchronization adjustment amounts are always equal can form a synchronization terminal group, which is set as a synchronization terminal group B. T may be set to 0.5 seconds, for example.

Step 402, the base station allocates a SYNC-RNTI for the synchronization terminal group B, and notifies all terminals of the synchronization terminal group B of the SYNC-RNTI through RRC signaling.

Step 403, the base station measures the uplink reference signals of all terminals of the synchronization terminal group B, and selects the uplink frame synchronization time adjustment quantity with the largest quantity among the obtained uplink frame synchronization time adjustment quantities of all terminals as the uplink frame synchronization time adjustment quantity of the whole synchronization terminal group.

And step 404, the base station transmits the uplink time advance TA of the synchronization terminal group B through the MAC CE, and the PDCCH corresponding to the MAC CE is identified by using the SYNC-RNTI.

Step 405, all terminals of the synchronization terminal group B receive the PDCCH according to SYNC-RNTI and interpret the TA value, thereby completing uplink synchronization.

Step 406, the base station keeps periodic measurement of uplink reference signals of all terminals of the synchronization terminal group B to track the change of the absolute uplink synchronization adjustment amount; if the number of times that the uplink synchronization absolute time adjustment amount of one terminal in the synchronization terminal group B and the uplink synchronization absolute time adjustment amount of the synchronization terminal group B occur differently reaches a certain preset threshold M1 within a period of preset time T1, the base station sends a dedicated signaling to notify the terminal to remove the terminal from the synchronization terminal group B. T1 may be set to 2 seconds, for example, and M1 may be set to 3 times, for example.

Step 407, after receiving the notification, the terminal releases the SYNC-RNTI corresponding to the synchronization terminal group B.

Example 4:

the present invention can be applied to other communication systems requiring uplink synchronization, such as TD-SCDMA or WiMax systems, and the specific implementation is similar to embodiments 1, 2 and 3, and will not be described again here.

A system for uplink synchronization of multiple terminals, the system comprising: a selection unit and an uplink synchronization unit. The selection unit is used for selecting the terminals with the same uplink synchronization information from the plurality of terminals; and the uplink synchronization unit is used for keeping the uplink synchronization of the selected terminals uniformly.

Here, the selecting unit is further configured to select a terminal having the same uplink frame synchronization time adjustment amount among the plurality of terminals. The system also comprises a determining unit, wherein the determining unit is used for determining the terminals with the same uplink frame synchronization time adjustment amount as a synchronization terminal group.

Here, in the sending stage when performing unified uplink synchronization maintenance, the uplink synchronization unit further includes a sending module, where the sending module is configured to set one or more network identifiers on a network side, and the base station selects a network identifier corresponding to the synchronization terminal group from the set network identifiers; the base station sends the selected network identification to all terminals in the synchronous terminal group; and the base station sends the uplink frame synchronization time adjustment quantity to all terminals in the synchronization terminal group.

Here, in the receiving stage when performing unified uplink synchronization maintenance, the uplink synchronization unit further includes a receiving module, where the receiving module is configured to synchronize all terminals in the terminal group to receive the corresponding uplink frame synchronization time adjustment amount according to the received network identifier.

Here, the selection unit further realizes the selection by means of presetting on the base station side. The preset mode of the base station side comprises any one of the following modes:

mode 1: the presetting module is used for setting the uplink frame synchronization absolute time adjustment quantity of the two terminals to be the same when the distance between the two terminals is smaller than a preset threshold.

Mode 2: the presetting module is used for setting the uplink frame synchronization absolute time adjustment quantity of a group of terminals to be the same when the distances from the group of terminals to the center position are all smaller than a preset threshold.

Mode 3: the presetting module is used for setting the uplink frame synchronization absolute time adjustment quantity of a group of terminals to be the same when the distance between each two terminals is smaller than a preset threshold.

Here, the selection unit further performs the selection by means of base station side measurement. The mode of the base station side measurement comprises any one of the following modes:

mode 1: the measuring module is used for measuring the uplink frame synchronization time adjustment quantity required by each terminal in the plurality of terminals to keep uplink synchronization by the base station; when the uplink frame synchronization absolute time adjustment quantities of the plurality of terminals are found to be equal in a preset time period or the number of continuous equal times exceeds a preset threshold, the uplink frame synchronization absolute time adjustment quantities of the plurality of terminals are known to be the same, and a synchronization terminal group is formed.

Mode 2: the measuring module is used for measuring the uplink frame synchronization time adjustment quantity required by the current terminal to maintain uplink synchronization in the plurality of terminals by the base station, and comparing the measured uplink frame synchronization time adjustment quantity of the current terminal with the uplink frame synchronization time adjustment quantity of the existing synchronization terminal group; when the uplink frame synchronization absolute time adjustment quantity of the current terminal is found, and the uplink frame synchronization absolute time adjustment quantity of the synchronization terminal group are kept equal in a preset time period or continuously equal times exceed a preset threshold, the uplink frame synchronization absolute time adjustment quantities of the current terminal and the synchronization terminal group are known to be the same, and the terminal can join the synchronization terminal group.

Here, the chinese and english explanations of the above-mentioned characters are as follows: a User Equipment (UE); timing Advance (TA for short).

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims

1. A method for uplink synchronization of multiple terminals is characterized in that the method comprises the following steps: selecting a terminal with the same uplink synchronization information from a plurality of terminals; and performing unified uplink synchronization maintenance on the selected terminals.

2. The method of claim 1, wherein the uplink synchronization information comprises: adjusting the uplink frame synchronization time; the method further comprises the following steps: and determining the terminals with the same uplink frame synchronization time adjustment amount as a synchronization terminal group.

3. The method of claim 2, wherein during the sending phase when performing the unified uplink synchronization maintenance, the method further comprises: the network side sets one or more network identifications, and the base station selects one network identification corresponding to the synchronous terminal group from the set network identifications; the base station sends the selected network identification to all terminals in the synchronous terminal group; and the base station sends the uplink frame synchronization time adjustment quantity to all terminals in the synchronization terminal group.

4. The method of claim 3, wherein during a receive phase when performing the unified uplink synchronization hold, the method further comprises: and all the terminals in the synchronous terminal group receive corresponding uplink frame synchronous time adjustment quantity according to the received network identification.

5. The method of claim 4, wherein the uplink frame synchronization time adjustment comprises: adjusting quantity of uplink frame synchronization relative time or adjusting quantity of uplink frame synchronization absolute time; wherein, the uplink frame synchronization relative time adjustment amount is: relative adjustment value of the adjustment quantity of the uplink frame synchronization absolute time relative to the current terminal;

6. The method of claim 2, further comprising: selecting terminals with the same uplink frame synchronization time adjustment amount from a plurality of terminals in a preset mode at a base station side;

7. The method of claim 2, further comprising: selecting terminals with the same uplink frame synchronization time adjustment amount from a plurality of terminals in a base station side measurement mode;

8. The method of claim 3, wherein when the base station sends the selected network identifier to all terminals in the synchronized terminal group, the method further comprises: the network identifier is sent through a Radio Resource Control (RRC) dedicated signaling, or the network identifier is sent through a Media Access Control (MAC) control unit, or the network identifier is sent through a physical downlink control channel.

9. The method of claim 3, wherein before the base station sends the uplink frame synchronization time adjustment to all terminals in the synchronization terminal group, the method further comprises obtaining the uplink frame synchronization time adjustment;

10. The method of claim 3, wherein when the base station transmits the uplink frame synchronization time adjustment to all the terminals in the synchronized terminal group, the method further comprises: the uplink frame synchronization time adjustment quantity is sent through a physical downlink control channel; the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

11. The method of claim 3, wherein when the base station transmits the uplink frame synchronization time adjustment to all the terminals in the synchronized terminal group, the method further comprises: the uplink frame synchronization time adjustment quantity is sent through a physical downlink shared channel indicated by a physical downlink control channel; the physical downlink control channel needs to be identified by a network identifier corresponding to the synchronization terminal group.

12. The method according to claim 2, 3 or 4, wherein the uplink frame synchronization time adjustment amount is specifically an uplink frame synchronization absolute time adjustment amount; the method further comprises the following steps: when the base station keeps measuring the uplink reference signal or the uplink synchronous signal of the mobile terminal with unlimited area in the synchronous terminal group, if the uplink frame synchronous absolute time adjustment quantity of the current terminal is judged to be asynchronous with the uplink frame synchronous absolute time adjustment quantity of the synchronous terminal group, the current terminal is removed from the synchronous terminal group.

13. The method of claim 12, wherein determining the out-of-sync comprises:

14. The method of claim 12, wherein determining the out-of-sync comprises: when the base station measures the uplink frame synchronization absolute time adjustment quantity of the current terminal and the occurrence of different continuous times of the uplink frame synchronization absolute time adjustment quantity of a synchronization terminal group to which the current terminal belongs reaches a preset threshold, judging that the current terminal is out of synchronization with the synchronization terminal group; wherein the preset threshold is an integer greater than 0.

15. The method of claim 12, wherein removing the current terminal from the group of synchronized terminals comprises: the base station informs the current terminal through a special signaling, and the current terminal releases the network identification corresponding to the synchronous terminal group after receiving the special signaling.

16. The method of claim 12, wherein removing the current terminal from the group of synchronized terminals comprises: and the base station sends the uplink frame synchronization absolute time adjustment amount to the current terminal in a conventional mode, and after receiving the uplink frame synchronization absolute time adjustment amount, the current terminal determines that the current terminal is removed from the synchronization terminal group and releases the network identifier corresponding to the synchronization terminal group.

17. A system for uplink synchronization of multiple terminals, the system comprising: a selection unit and an uplink synchronization unit; wherein,

18. The system according to claim 17, wherein the selecting unit is further configured to select a terminal with the same uplink frame synchronization time adjustment amount from the plurality of terminals;

19. The system according to claim 18, wherein in the sending phase when performing the unified uplink synchronization maintenance, the uplink synchronization unit further includes a sending module, configured to set one or more network identifiers on the network side, and the base station selects a network identifier corresponding to the synchronization terminal group from the set network identifiers; the base station sends the selected network identification to all terminals in the synchronous terminal group; and the base station sends the uplink frame synchronization time adjustment quantity to all terminals in the synchronization terminal group.

20. The system according to claim 19, wherein in a receiving phase when performing the unified uplink synchronization maintenance, the uplink synchronization unit further includes a receiving module, configured to receive corresponding uplink frame synchronization time adjustment amounts by all terminals in the synchronization terminal group according to the received network identifier.

21. The system according to claim 18, wherein the selection unit further implements the selection by means of pre-setting at the base station side;

22. The system according to claim 18, wherein said selection unit further enables said selection by means of base station side measurements;